Safety device and method



March 3, 1970 G. E. NORRED SAFETY DEVICE AND METHOD Filed April 4, 1968 IN VEN TOR. GLENN E. NORRED BY EMMM ATTORNEYS United States Patent Office 3,499,130 Patented Mar. 3, 1970 US. Cl. 20ll61.04 7 Claims ABSTRACT OF THE DISCLOSURE In an engine having an oil case for lubricating the engine parts, a method for stopping the engine when the oil in the case falls below a predetermined level; the method employing a plug having a pair of electrodes extending int-o the oil case to be insulated from each other by the oil when at a satisfactory level in the case. One of the electrodes is connected to the spark plug of the engine while the other is connected to ground so that when the level of the oil falls out of contact with the electrodes, an arc will be passed across the electrodes shunting the spark plug and thereby stopping operation of the engine.

SUMMARY OF INVENTION AND OBJECTS This invention generally relates to a safety device and method for preventing damage to an engine or motor as a result of insutficient lubrication. Although the present invention is particularly suitable for small, four-cycle engines such as used on lawn mowers and garden or farming equipment, the present invention has equal applicability elsewhere.

One of the objects of the present invention is to pro vide a new method and an associated safety device for preventing damage to an engine as a result of an insufficient supply of lubricant.

A further object of the present invention is to provide a novel method and an associated safety device for stopping an engine in operation when the oil in the oil case of the engine falls below a predetermined safe level. Included herein is the provision of such a method and safety device which will stop the engine automatically, that is, with-out any manual operation or supervision.

A still further object is the provision of such a safety device which may be economically manufactured and easily incorporated into standard or conventional engines without sacrificing performance or encumbering the engine.

In one embodiment of the invention, the foregoing objects are achieved by a plug that is screwed into the oil case of the associated engine, The plug has two electrodes which extend into the oil case so as to be insulated from each other by the oil when the oil is at a satisfactory level. One electrode is connected to ground while the other is connected to the ignition circuit preferably the spark plug. When the level of the oil is suh'icient, the electrodes are insulated from each other by the oil and there is no effect on the ignition system. However when the oil level drops below a predetermined satisfactory level, the electrodes will no longer be insulated and an arc will pass between them shunting the spark plug and stopping the engine.

Other objects and advantages of the present invention will become apparent from the following more detailed description taken in conjunction with the attached drawing which is a side elevational view of an engine incorporating the safety device of the present invention, portions of the oil case in the engine being broken away to show the safety device.

DETAILED DESCRIPTION Referring now to the drawings in detail, there is shown a safety plug generally designated 10 embodying the present invention employed together with an engine 12 having a typical spark plug 14 and an oil case 16 containing oil 17.

Safety plug 10 is secured in oil case 16 preferably in the oil filler hole 18. Plug 10 may be made from a suitable'plastic and includes a head portion 20 positioned externally of case 16 and a cylindrical bottom portion 22 which projects from the head portion into the oil case. Cylindrical portion 22 forms a chamber 24 having an open lower end 26 to permit oil to enter into the chamber as illustrated in the drawings. In the preferred embodiment shown, the external wall of cylindrical portion 22 is formed at its upper portion with threads 28 engageable with corresponding threads formed in the oil filler hole 18 to secure the plug in the case. Between head portion 20 and cylindrical portion 22 there is an annular shoulder 30 which receives an annular sealing gasket 32 that is pressed against the oil case when the safety plug is secured. Sealing washer or gasket 32 is made from a conductive material such as copper for purposes which will become apparent.

In accordance with the invention, the plug is provided with a pair of electrodes 34 and 36 secured in head portion 20 and projecting from the latter downwardly into the chamber 24 in spaced relationship. Preferably, the extremities of the electrodes are spaced inwardly from open end 26 of cylindrical portion 22. For reasons described below, it is also preferred that the electrodes be formed with reentrant hook-like portions at their ex tremities such as those designated 34a and 36a in the drawings. One electrode 36 which may be termed the positive electrode, is connected to ground such as by the element 38 which interconnects electrode 36 and the metallic gasket 32. Element 38 may be formed integral with electrode 36 or may be a separate Wire connected to the electrode and the metallic washer 32.

The other electrode 34 which may be termed the negative electrode is connected to the ignition system of the engine, preferably the spark plug 14, by means of a terminal stud 40 secured in head portion 20 and project ing outwardly from the top thereof. A conductor 42 interconnects stud 40 and electrode 34; the conductor 42 may be integral with electrode 34 or may be a wire. Connecting spark plug 14 and stud 40 is a Wire 44.

In the shown embodiment, a plastic insert sleeve 50 is employed to secure stud 40 in head portion 20. Sleeve 50 has threads 52 received in corresponding threads formed in a passage which extends through the top of head portion 20. The outer end of stud 40 is threaded, and a pair of nuts 56 are employed to secure the end of wire 44 on stud 40.

In operation, when the oil 17 in the case is at a satisfactory or safe level as indicated by 46, electrodes 34 and 36 will be insulated from each other and there will be no effect on the ignition of the engine, However, when the oil falls below the safe level and no longer contacts the electrodes, as indicated by 48, an arc will be passed between the electrodes shunting the spark plug 14 and thus causing the engine to come to a stop; assuming of course that the engine was in operation. The spacing between the electrodes is chosen so as to produce the desired arcing and it will be understood that this spacing may vary depending on the voltage through the ignition system. The reentrant portions 34a and 36a of the electrodes insure that by the time the oil level drops out of contact with the electrodes to level 48 for example, oil will have drained off the tips of the reentrant portions. In this way, the tips of the electrodes will be free of any oil droplets and eflective and unimpeded arcing will take place across the electrodes to insure stoppage of the engine.

Moreover in the shown embodiment, a vent hole 27 is provided in cylindrical portion 22 to allow air to escape from the chamber 24 so that the level of the oil in chamber 24 will be the same as that outside chamber 24. However, it is possible to construct a satisfactory safety plug in accordance with the invention without such a vent hole but with the length of the electrodes calibrated such that when the level of the oil in chamber 24 falls below the extremities of the electrodes, the level of oil in the surrounding case will be insuflicient and the engine will be stopped despite any difference between the oil levels inside and outside of chamber 24.

In addition to the application described above, it will be appreciated that the safety plug may be connected to a measuring or indicating device to provide a signal when the oil falls below a predetermined level. Additionally, the safety plug may be used to sense the level of fluids other than oil as long as the fluids are sufficiently nonconductive to insulate the electrodes from each other.

In addition to the objects mentioned above, it will be seen that the safety plug may be easily removed from the oil case for cleaning or replacement. It will also be apparent that the safety plug may be manufactured from standard parts at low cost.

What is claimed is:

1. A device for determining when a generally nonconductive fluid in a case is below a predetermined level; the device comprising a body adapted to be secured in an opening in an associated ease containing a generally nonconductive fluid, said body including a portion defining an open ended chamber adapted to extend into the case and to receive portions of the fluid when the body is attached to the case, a pair of positive and negative electrodes fixed to the body and extending into said chamber in spaced relationship so as to be insulated from each other by the fluid in the case when the fluid is at a predetermined level, means for connecting the positive electrode to a ground, terminal means fixed to the body for connection to an electrical circuit, and means connecting the terminal means to the negative electrode, said electrodes being spaced from each other such that when they are not insulated by the fluid and the circuit is energized an arc will pass between them causing deenergization of the circuit, said electrodes each having mutually facing reentrant portions which extend upwardly from low points on the electrodes and terminate in extremities positioned above the low points of the electrodes to insure drainage of oil from the extremities of the electrode when the oil level in the associated fluid case drops below a predetermined amount.

2. The device defined in claim 1 wherein said portion has a generally cylindrical shape and includes means for securing the device to the case containing the nonconductive fluid.

3. The device defined in claim 2 wherein said portion is made from plastic and wherein said means for connecting the device to the case includes threads formed in said portion.

4. The device defined in claim 3 wherein said body further includes an external radial shoulder, and wherein said means for connecting the positive electrode to ground includes a metallic washer received about said portion in engagement with said shoulder so as to contact the case when the device is secured therein.

5. The device defined in claim 4 wherein said body .further includes a head portion located opposite said References Cited UNITED STATES PATENTS 1,548,366 8/1925 Johnson. 1,280,762 10/191 8 Kloman.

FOREIGN PATENTS 353,559 10/1937 Italy.

WENDELL E. BURNS, Primary Examiner US. Cl. X11. 

